Parse out the optional value objects.

src/types/affiliated_keyword.rs

@@ -6,7 +6,7 @@ use super::Object;
 pub enum AffiliatedKeywordValue<'s> {
     SingleString(&'s str),
     ListOfStrings(Vec<&'s str>),
-    ListOfListsOfObjects(Vec<Vec<Object<'s>>>),
+    ListOfListsOfObjects(Vec<(Option<Vec<Object<'s>>>, Vec<Object<'s>>)>),
 }
 
 #[derive(Debug)]